The present invention relates generally to communication receivers and, more specifically, to a Transmission Parameter Signaling (TPS) decoder in orthogonal frequency division multiplexing (OFDM) receivers.
The following disclosure will describe a digital video broadcasting (DVB) receiver for digital terrestrial television (DTV). The concepts are equally applicable to any other channels of transmission of DTV receivers and to other receivers or standards using orthogonal frequency division multiplexing (OFDM). These may include but not be limited to wireless standards worldwide, such as wireless LAN 802.11a and g, HIPERLAN/2, Digital Audio Broadcasting (DAB), Digital Video Broadcasting Terrestrial (DVB-T), Digital Video Broadcasting for handheld (DVB-H), 802.16 Broadband Wireless Access, etc. The European terrestrial DTV standard DVB-T (ETS 300 744) is based on COFDM technologies to combat multipath fading. See ETSI EN 300 744 V.1.4.1 “Digital Video Broadcasting (DVB): Framing structures, channel coding, and modulation for digital terrestrial television.”
FIG. 1 shows a block diagram for a typical DVBT receiver. The digital signal processing for a DVBT receiver can be partitioned into three portions. The first portion 10 includes an RF front end 12, and A/D converter 14, an OFDM demodulator 16, a demodulation 18 and a pilot and TPS decoder 19. This receiver front-end signal processing portion performs receiver training, including various synchronization and channel estimation and OFDM demodulation. The second portion 20 is the DVBT receiver back-end signal processing block. It performs DVBT inner channel decoding and outer channel decoding. The third portion 30 is a MPEG Decoder. An example is shown in U.S. Pat. No. 6,687,315.
The Transmission Parameter Signaling (TPS) is a signaling scheme used in DVB type systems, such as DVB-T and the coming DVB-H, to carry signaling information to the receiver the parameters related to the transmission scheme, i.e., channel coding and modulation. In DVB-T, the TPS signaling is transmitted in parallel on 17 TPS carriers for the 2K mode and on 68 carriers for the 8K mode. Every TPS carrier in the same symbol conveys the same differentially encoded information bit. The TPS is defined over 68 consecutive OFDM symbols (one OFDM frame), each OFDM symbol conveys 1 TPS bits, and each TPS block (transmitted over 68 OFDM symbols) contains 68 bits. Every TPS carrier in an OFDM symbol is DBPSK modulated and conveys the same message. The DBPSK is initialized at the beginning of each TPS block.
In the OFDM receiver front-end signal processing 10 of FIG. 1, each received OFDM symbol is extracted from the received data sequence at proper sampling timing and symbol timing instances. The extracted OFDM symbol I/Q in time domain will go through the OFDM demodulator 16 (an FFT operation) to generate the subcarriers in frequency domain. The OFDM symbol in frequency domain will go through channel correction to remove the channel effects. At the DVB receivers, the TPS DBPSK decoding/demodulation is performed on the subcarriers after the channel correction. Each received TPS block will go through BCH error decoding to get the error corrected TPS information bits. The TPS information bits are used to set up the receiver parameters to enable the receiver to function properly.
The TPS reception must be extremely reliable and robust in the presence of noise and fading. There are two levels of protection defined for the TPS transmission scheme. First, the TPS transmission is equipped with frequency diversity: 1 TPS bit is transmitted on 17 scattered subcarriers in an OFDM symbol for the 2K mode, so if selective frequency fading exists, there is a good chance that not all of the scattered 17 subcarriers are in deep fading, it is still possible to demodulate the correct TPS bits. The BCH(67,53,t=2) error correction coding provides the second layer of error protection for each TPS block. It is designed to correct up to two error bits in one encoded TPS block.
However, it is found in DVB system simulation that even with the above two levels of protection for TPS transmission as defined in DVB specification, TPS reception failures still occur intermittently in severe fading and high noise conditions. One example is that the conventional TPS reception algorithm fails sometimes at SNR=6 dB and Rayleigh fading channel.
Due to computational complexity and high MIPs required for the DVBT receiver, until recently, DVBT receivers have been implemented in hardware using ASICs. In the case of multi-protocol communication systems, the hardware implementation becomes less attractive due to extra chip cost and PC board area consumed. In this disclosure, an improved software implementation of a DVBT receiver is described. In this design, all functions associated with the DVBT receiver may be implemented in software in the Sandbridge Technologies Multithreaded SB9600 processor. The device may be used in hand-held devices, such as mobile phones and PDAs.
The present receiver includes an A/D converter for converting received analog signals to a digital signal data stream and an OFDM demodulator for producing a set of complex I and Q components of subcarriers from the digital signal data stream. A CSI estimator for estimating Channel State Information (CSI) from the sets of complex I and Q components and a TPS decoder for decoding TPS data from the sets of complex I and Q components using the CSI are provided. The receiver may also include a Viterbi decoder for decoding the sets of complex I and Q components using the CSI.
A method of decoding TPS data in a receiver includes estimating CSI from the sets of complex I and Q components of subcarriers of an OFDM signal demodulated in the receiver; and decoding TPS data in the sets of complex I and Q components of subcarriers using the CSI. The method may further include Viterbi decoding the sets of complex I and Q components using the CSI.
These and other aspects of the present disclosure will become apparent from the following detailed description of the disclosure, when considered in conjunction with accompanying drawings.